Hey dude,
u can make fifa 15 smother by going to task manager-details then u want to run fifa 15 game then go back to task manager and select fifa 15 from detals and right click and select set priorty,It will be in normal(default)
u have to change it to high ,if high is having lag set it to real time you have to have a decent system, it can be done with most of the game if u want a video feel free to ask